In 1387 Dec 29, Henricus, episcopus Norwicen (Henry, bishop of Norwich) was granted, by Richard II, (In year 11 of his reign) a Royal licence to crenellate Gaywode (Gaywood Hall, Kings Lynn)

"Licence for the king's kinsman, Henry, bishop of Norwich, to crenellate his manors (manerium) of North Elmam and Gaywode, co. Norfolk."

Granted at Westminster, by privy seal.

Licence to crenellate granted to Henry, bishop of Norwich in 1388. This licences was also the one which produced the fortified house of North Elmham.

Original source is

• Calendar of Patent Rolls (1385-89) p381

(In fact, the original source given is usually a transcription/translation of what are precious medieval documents not readily availably. It should be noted that these transcription/translations often date to the nineteenth or early twentieth centuries and that unwitting bias of transcribers may affect the translation. Care should also be taken to avoid giving modern meaning to the medieval use of certain stock words and terms.)

Significant later source are;

• Thompson, M.W., 1998, Medieval bishops' houses in England and Wales (Aldershot: Ashgate Publishing) p168
  Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol3 pt2 p420

More details about licences to crenellate can be found here.

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